Princes William and Harry have opened up about the awful moment they were told of Princess Diana's death and the pain and confusion in the days that followed.

Prince Harry paid tribute to his father Prince Charles for the care he showed to his sons in the aftermath of her death, describing how he was "there for us."

The royal brothers made their heartbreaking testimonies in a BBC documentary titled Diana, 7 Days, which also features insight from Diana’s family including her sister Lady Sarah McCorquodale and former Prime Minister Tony Blair.

Harry said about his initial reaction to being told, while at Balmoral, that his mother was dead: “Disbelief, refused to accept it.

“There was no sort of sudden outpour of grief.”

He added about Prince Charles: “One of the hardest things for a parent to have to do is to tell your children that your other parent has died.

“How you deal with that I don’t know.

This photograph released by Kensington Palace, from the personal photo album of the late Diana, Princess of Wales, shows the princess holding Prince William whilst pregnant with Prince Harry (Image: The Duke of Cambridge and Prince Harry)

“But, you know, he was there for us.

“He was the one out of two left and he tried to do his best and to make sure that we were protected and looked after.

“But, you know, he was going through the same grieving process as well.”

“And you keep asking yourself ‘why me?’ all the time ‘why, what have I done? why, why has this happened to us?’.”

This photograph released by Kensington Palace, from the personal photo album of the late Diana, Princess of Wales, shows Prince William and Prince Harry in borrowed policemen outfits, and featured in an ITV documentary. Photo credit: The Duke of Cambridge and Prince Harry.

The documentary also reveals the princes’ conflicted feelings at walking behind their mother's coffin aged just 15 and 12.

They had to greet screaming and grieving crowds after her death, and also revealed how they suppressed their emotions so they were never seen crying in public.

William said about viewing the flowers and notes outside the gates of Balmoral: “I was very touched by it but none of it sank in.

“All I cared about was I’d lost my mother and I didn’t want to be where I was...

“When we go out and do things like that, in order not to completely and utterly break down we have to put on a bit of a game face.

“And you have to be quite strong about it because otherwise you’re a walking mess.”

Harry added: “Looking back now probably the last thing I wanted to do was read what other people were saying about my mother.

“Yes it was amazing, it was incredibly moving to know, but at that point I wasn’t there.

“I was still in shock.”

Prince William and Prince Harry sitting on a picnic bench together (Image: The Duke of Cambridge and Prince Harry)

He added that suppressing his emotions in public has had a lifelong effect, saying: “If someone tried to get me to cry in public I couldn’t.

“And that’s probably from all of that, from whatever happened then has changed me in that sense.”

The princes also praised The Queen for her decision to keep them away from the spotlight in the first few days, despite growing public pressure to return to London.

Harry said: “It was a case of ‘how do we let the boys grieve in privacy but at the same time when is the right time for them to put on their prince hats and carry out duties'."

William said: “I think it was a very hard decision for my grandmother to make.

“She felt very torn between being a grandmother to William and Harry and her Queen role.”

But when they did eventually return to Kensington Palace, the brothers reveal how “peculiar” they found the wailing from the crowds who had never met their mother.

And Harry added: “What we were doing, what was being asked of us was verging on normal then.

“But now it’s like, ‘you did what?’.”

The brothers described the decision to walk behind Diana’s coffin as a “group” one with William adding: “It wasn’t an easy decision”.

He described it as “one of the hardest things I’ve ever done” and “a very long, lonely walk”, adding: “The balance between me being Prince William and having to do my bit versus the private William who just wanted to go in a room and cry because he’d lost his mother.

“I just remember hiding behind my fringe...

“It was kind of like a little tiny bit of safety blanket.

“I know it sounds ridiculous but at the time I felt if I looked at the floor with my hair in my face no-one could see me.”

Harry said: “I was just so focussed on getting it done and doing everything that was asked of me there and then and making sure that I did my mother proud.”

William said: “There is this element of duty and responsibility that you have to do things you don’t want to do.

“But I have to say that whenever it becomes that personal as walking behind your mother’s funeral cortege it gets to another level of duty.

Prince Harry and William

“But I just kept thinking about what she would want and that she’d be proud of Harry and I being able to go through it.”

Harry also revealed that he struggled to contain his emotions during the funeral service.

He said: “When the shutters came down and I refused to let myself get sad about the fact that my mother had died there was certain things that there was like someone firing an arrow straight into that barrier and the head of it getting through.

“And Elton John’s song was incredibly emotional.

“That was part of this whole trigger system which nearly brought me to the point of crying in public, which I didn’t do.”

And William said about the public grief: “I couldn’t understand why everyone wanted to cry as they did and show such emotion as they did when they didn’t really know out mother.

“I did feel a bit protective at times about that.

“I was like, you didn’t even know her, why and how are you so upset.”

The brothers also spoke out about the intense scrutiny Diana faced throughout her life and in death.

“I think one of the hardest things to come to terms with is the fact that the people that chased her into the tunnel were the same people that were taking photographs of her while she was still dying on the back seat of the car," Harry said.

Princess Diana with sons Harry and William

In the documentary, the princes both revealed that, 20 years on, they understand more than ever what Diana gave the world and want to continue her legacy.

Harry said: “Years after I spent a long time in my life with my head buried in the sand thinking I don’t want to be Prince Harry, I don’t want this responsibility, I don’t want this role. Look what’s happened to my mother, why does this have to happen to me.

“But now all I want to do is try and fill the holes that my mother has left and that’s what it’s about for us is trying to make a difference and in making a difference, making her proud.

“She was the Princess of Wales and she stood for so many things but deep down inside for us she was a mother.

“And we will miss our mother and I wonder every single day what it would be like having her around.”

William added: “I wouldn’t let it break me, I wanted it to make me.

“I wanted her to be proud of the person I would become and I didn’t want her worried or her legacy to be that William or Harry were completely and utterly devastated by it.

“She loved Harry and I dearly, even so that I can sit here after 20 years and I still feel that love.

"I still feel that warmth 20 years on which is a huge testament to her.

“If I can be even a fraction of what she was I’ll be proud and I’ll hopefully make her proud in what I’ve done.”